Otoacoustic Emissions VI. Experimental use of Otoacoustic EOAEEmissions in the Guinea Pig

Overview

Evoked otoacoustic emissions can be detected in the majority of subjects with normalhearing. They are used currently in the diagnosis of peripheral hearing disorders and are used alsoin audiological research. Extensive clinical research is impossible without a background of experi-mental modelling of pathological conditions in laboratory animals. The authors elaborated a methodfor EOAE examination in guinea pigs using the ILO 92 apparatus. It was revealed that the responsedepends to a considerable extent on parameters of assessment. For examination of TEOAE in guineapigs stimulation by a non-linear click with intensities up to 75 dB SPL and an averaging window of1.5-10 ms is best. For examination of DPOAE the authors recommend stimulation with intensitiesLI = 55 dB SPL, L2 = 45 dB SPL, ratio of frequencies f2/f1 = 1.209. The intravital origin of thusobtained EOAE responses was tested by post-mortem experiments. TEOAE produced by a click withan intensity of 74.4 dB SPL could not be elicited even after one minute. DPOAE 55/45 three minutesafter extinction of respiration. Conversely DPOAE elicited by primaries 70/70 persisted for at least14 minutes after extinction of cardiac activity. The authors found furthermore in a group of guineapigs that contralateral acoustic stimulation by broad-spectrum noise with an intensity of 61 dB SPLhas a comparable effect on TEOAE as electric stimulation of the contralateral oval window. Sup-pression of the amplitude of TEOAE on average by 0.87 ± 0.55 dB and 0.79 ± 0.87 dB resp. occurred.Electric stimulation of the ipsilateral colliculus inferior did not produce a significant effect. Possiblesuppression of TEOAE by contralateral electric stimulation of the round window is a model suitablefor research of the function of the efferent system.

Key words:
evoked otoacoustic emissions, contralateral acoustic and electric suppression, guineapig.